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The invention generally relates to draft inducers and, in particular, a control for a fan driven motor for inducing a draft in an exhaust.
In a conventional furnace, the exhaust gases from the combustion chamber are carried away by natural convection currents. However, the resultant loss of heat energy in the exhaust gases decreases the overall efficiency of the furnace. In order to improve the efficiency, heat exchangers have been used to extract additional heat from the exhaust gases prior to the time they are vented to the atmosphere. This cools the exhaust gases which reduces the natural convection currents which would otherwise carry the gases away. One solution has been to use a draft inducing fan to exhaust the exhaust gases into the atmosphere.
Prior designs for a draft inducer control system for controlling the exhaust of a furnace have included a pressure transducer located in the venting adjacent the combustion chamber, a speed sensor for the motor, and a torque sensor for the motor. These components have been used to vary the induced draft as a function of the sensed pressure in the combustion chamber. Such a control system is disclosed in U.S. Pat. No. 5,075,608 to David M. Erdman, for example.
While such systems represent an improvement, further improvements in draft inducer control systems, draft inducer apparatus, and methods of control and operation can beneficially increase the efficiency of a furnace. For example, improvements which allow the speed/torque of the motor and the magnitude of the induced draft to be preselected for given operating conditions of the furnace would increase efficiency by more closely matching the induced draft to the requirements of the furnace. Improvements which, allow the preselecting to occur quickly and economically during manufacture or installation of the furnace would also be desirable. Greater versatility of the draft inducer control system in responding to various control signal conditions would also be desirable.